Merge pull request matthewsamuel95#798 from abhineet1729/master

Added Intersection point of two Linked Lists

Author: matthewsamuel95

Data Structures/Linked List/Intersection point of two Linked Lists.cpp

@@ -0,0 +1,135 @@
+/* Algorithm
+1) Get count of the nodes in the first list, let count be c1.
+2) Get count of the nodes in the second list, let count be c2.
+3) Get the difference of counts d = abs(c1 – c2)
+4) Now traverse the bigger list from the first node till d nodes so that from here onwards both the lists have equal no of nodes.
+5) Then we can traverse both the lists in parallel till we come across a common node. (Note that getting a common node is done by comparing the address of the nodes)
+*/
+
+#include<stdio.h> 
+#include<stdlib.h> 
+
+/* Link list node */
+struct Node 
+{ 
+int data; 
+struct Node* next; 
+}; 
+
+/* Function to get the counts of node in a linked list */
+int getCount(struct Node* head); 
+
+/* function to get the intersection point of two linked 
+lists head1 and head2 where head1 has d more nodes than 
+head2 */
+int _getIntesectionNode(int d, struct Node* head1, struct Node* head2); 
+
+/* function to get the intersection point of two linked 
+lists head1 and head2 */
+int getIntesectionNode(struct Node* head1, struct Node* head2) 
+{ 
+int c1 = getCount(head1); 
+int c2 = getCount(head2); 
+int d; 
+
+if(c1 > c2) 
+{ 
+	d = c1 - c2; 
+	return _getIntesectionNode(d, head1, head2); 
+} 
+else
+{ 
+	d = c2 - c1; 
+	return _getIntesectionNode(d, head2, head1); 
+} 
+} 
+
+/* function to get the intersection point of two linked 
+lists head1 and head2 where head1 has d more nodes than 
+head2 */
+int _getIntesectionNode(int d, struct Node* head1, struct Node* head2) 
+{ 
+int i; 
+struct Node* current1 = head1; 
+struct Node* current2 = head2; 
+
+for(i = 0; i < d; i++) 
+{ 
+	if(current1 == NULL) 
+	{ return -1; } 
+	current1 = current1->next; 
+} 
+
+while(current1 != NULL && current2 != NULL) 
+{ 
+	if(current1 == current2) 
+	return current1->data; 
+	current1= current1->next; 
+	current2= current2->next; 
+} 
+
+return -1; 
+} 
+
+/* Takes head pointer of the linked list and 
+returns the count of nodes in the list */
+int getCount(struct Node* head) 
+{ 
+struct Node* current = head; 
+int count = 0; 
+
+while (current != NULL) 
+{ 
+	count++; 
+	current = current->next; 
+} 
+
+return count; 
+} 
+
+/* IGNORE THE BELOW LINES OF CODE. THESE LINES 
+ARE JUST TO QUICKLY TEST THE ABOVE FUNCTION */
+int main() 
+{ 
+/* 
+	Create two linked lists 
+
+	1st 3->6->9->15->30 
+	2nd 10->15->30 
+
+	15 is the intersection point 
+*/
+
+struct Node* newNode; 
+struct Node* head1 = 
+			(struct Node*) malloc(sizeof(struct Node)); 
+head1->data = 10; 
+
+struct Node* head2 = 
+			(struct Node*) malloc(sizeof(struct Node)); 
+head2->data = 3; 
+
+newNode = (struct Node*) malloc (sizeof(struct Node)); 
+newNode->data = 6; 
+head2->next = newNode; 
+
+newNode = (struct Node*) malloc (sizeof(struct Node)); 
+newNode->data = 9; 
+head2->next->next = newNode; 
+
+newNode = (struct Node*) malloc (sizeof(struct Node)); 
+newNode->data = 15; 
+head1->next = newNode; 
+head2->next->next->next = newNode; 
+
+newNode = (struct Node*) malloc (sizeof(struct Node)); 
+newNode->data = 30; 
+head1->next->next= newNode; 
+
+head1->next->next->next = NULL; 
+
+printf("\n The node of intersection is %d \n", 
+		getIntesectionNode(head1, head2)); 
+
+getchar(); 
+}